July 24, 2009

As a result of the continuing high levels of toxicity in Maine and the sighting of a very large red water patch of Alexandrium cells near Portsmouth on July 10 and 11, an event response cruise was conducted from July 19 - 23, using funds generously supplied by the NOAA National Ocean Service (NOS; see NOAA press release). The purpose of this cruise was to ascertain the abundance and distribution of Alexandrium cells in western and eastern Gulf of Maine waters, to provide guidance to managers concerned with both inshore and offshore toxicity. Results of that survey are shown in the cell distribution map. Throughout the large area that was surveyed, Alexandrium cell concentrations were low - maximally 100 - 200 cells/L. This is in stark contrast to the high cell concentrations that were present earlier in the bloom, and in particular, to those measured in the red tide patch (approximately 1.7 million cells/L).

The cruise observations suggest that the 2009 Alexandrium bloom is nearly gone for much of the coasts of Maine, New Hampshire and Massachusetts. Several caveats are in order here. The first is that these low cell concentrations should not be interpreted to mean that shellfish are safe to consume. Shellfish species vary in their rates of detoxification, so shellfishermen and private citizens should refrain from harvesting any shellfish until state monitoring programs have reopened closed areas. There are still very dangerous levels of toxin in shellfish throughout the region.

The second caveat is that toxicity in eastern Maine is believed to be linked to Alexandrium blooms that occur within the Bay of Fundy. Those blooms are ongoing at this time, so there is a possibility that some cell populations can leave the Bay of Fundy and impact eastern Maine. Therefore, its premature to signal the end of the 2009 bloom for that region.

Note also that, although rare, fall blooms of Alexandrium do occur within the Gulf of Maine. In some past years, this has resulted in shellfish closures in September and even October.

Thus the 2009 bloom season appears to be winding down, but there are possibilities for a continuation or resurgence of toxicity in eastern sections this summer as well as for a second bloom event in the fall.

Looking back to the advisory we issued in April, in many ways this has been borne out since a significant regional event did occur that closed shellfish beds from the Canadian border to the middle of Massachusetts Bay, much as happened in 2006 - the year we used as an example in that advisory. However, there were aspects of the 2009 bloom that were not foreseen nor were they captured in our numerical model simulations, in particular, the high levels of toxicity throughout Maine, in contrast to the relatively low levels measured in Massachusetts. Its too soon for us to answer the question of why 2009 was so severe in Maine, and unfortunately this was not a year of GOMTOX cruises, thus we have very limited survey data to scrutinize for an answer. We do wonder whether the large amounts of rainfall as well as the lack of strong northeast winds (which can transport the Alexandrium populations from east to west) were factors in the observed toxicity patterns.

As for future cruises - we do not anticipate any additional survey work during this bloom period unless something unusual happens and the bloom increases dramatically. We will, however, be out again in October when we will map the abundance of Alexandrium resting cysts. In the past, we have found a very strong linkage between the abundance of these cysts and the magnitude of the Alexandrium bloom in the following year. It is thus too soon to speculate about what might lie in store for the region in 2010, but we will be working towards an advisory this winter and should make it public in the spring.

We wish to thank the National Ocean Service and all of the Congressional delegations who worked to obtain event response funding to provide valuable cell count information over the last week. This has been a difficult time for shellfishermen and many others in the region and it is welcome news that the outbreak is on the wane.